Heme proteins play an active role within a wide variety of biologically fundamental processes by carrying out selected functions. However, inadequate oxygen supply to various heme-proteins is a cause of human mortality and abnormalities. In this work, the heme-proteins to be studied extend from oxygen transport monomeric and tetrameric hemoglobins from Lucina pectinata and bovine, respectively, to oxygen reduction monomeric and dimeric cytochrome c oxidase from shark and bovine, respectively. For these systems ligand recognition leads to specific heme-ligand reactions. In solution, the details of how protein ligand selection and ligand affinity of oxygen (O2), carbon monoxide (CO), and nitric oxide (NO) correlate with protein and chromophore structural dynamics, environment and ligand orientation remains an area of unsolved problems. These conditions are important to understand the interaction between heme-proteins and O2, CO and NO when they carry out their diversified functions. The identification of properties which control ligand selection will provide support in the synthesis and development of artificial oxygen carriers. Elucidation of the structure-function relationship for monomeric, dimeric and tetrameric heme-proteins requires detailed knowledge of both the static and the dynamical behavior of the heme-protein-ligand complexes. Using our nanosecond time-resolved infrared spectroscopy (TRIR), ligands orientation and dynamics will e determined. Resonance Raman and FTIR will be employed to identify chromophore structure and ligand-metal isotopic vibrations. The frequencies (i.e. nuCO, nuFE-C and deltaFeCO) will be used to calculate the experimental "G determinant isotopic ration," (GDIR), while TRIR linear dichroism will be used to determine the angle ligand orientation relative to the heme plane normal. For the heme-proteins and their conformers, the experimental GDIR and ligand angles will be compared with plots of theoretical GDIR calculated as function of the ligand angle. The comparison will allow to distinguish the metal-ligand orientation (i.e. linear, bent, tilted or kinked) in heme-protein solutions. The unique aspects of our approach resides in the combination of TRIR, rR, FTIR, GDIR and monomeric, dimeric and tetrameric heme-proteins to study in solution ligand orientation ad selections process.